Typical normally closed solenoid valves have a biasing spring to seat a ball valve and thereby close the supply port when the solenoid is not energized. Thus, in order to open this valve, it is necessary for the solenoid to exert sufficient force on the ball to overcome the force of the spring.
In the solenoid valve of this invention, the ball valve for the supply port is held closed solely by the fluid pressure at the supply port. A spring is provided, but the spring does not engage the ball valve until after it is opened. When the current in the solenoid is interrupted, the fluid pressure in the supply passage, together with the force of the spring, return the ball to its seat.
In accordance with a specific embodiment of the invention about to be described, the valve housing has a supply passage, a control passage and an exhaust passage. A valve for the supply passage is provided to open and close communication between the supply passage and the control passage. This valve is normally held closed by the pressure of fluid in the supply passage. A valve for the exhaust passage controls communication between the control passage and the exhaust passage. A pintle is provided between the two valves. When the valve for the supply passage is closed, the pintle opens the valve for the exhaust passage, thereby opening communication between the control and exhaust passages. Energization of the solenoid closes the exhaust passage valve. This shifts the pintle which unseats the supply passage valve against the pressure of fluid in the supply passage.
In the preferred embodiment, the armature for the solenoid serves as the exhaust passage valve.
Preferably, the spring in the supply passage is a compression coil spring which is loosely captured between the supply passage valve and a stop in the supply passage. This valve, when seated, is spaced from the stop a distance which exceeds the length of the coil spring in its natural, free-state condition.
One object of this invention is to provide a solenoid valve having the foregoing features and capabilities.
Another object is to provide a solenoid valve which is constructed of a relatively few simple parts, is rugged and durable in use, and is capable of being inexpensively manufactured and assembled.
These and other objects, features and advantages of the invention will become more apparent as the following description proceeds, especially when considered with the accompanying drawings wherein: